Many conventional charge pumps circuits are push-pull style tri-stating charge pumps which have trouble operating at very high speeds. Push-pull style charge-pumps rely on precise matching between pull-up and pull-down currents. Furthermore, the PMOS transistors frequently used in pull-up stages are slow and thus limit the speed of operation. Previous charge-pump circuits also require extra circuitry to maintain an adequate common mode at the charge-pump outputs.
FIG. 1 illustrates one conventional charge-pump circuit 10. The charge-pump circuit 10 requires a separate multiplexer 12. The circuit 10 is limited to the use of the multiplexer 12.
FIG. 2 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,825,640. The push-pull style of charge-pump circuit of FIG. 2 relies on precise matching between pull-up and pull-down currents. The circuit is limited to the speed of PMOS transistor MP used in the pull-up stage. Furthermore the conventional charge-pump shown requires extra circuitry to maintain an adequate common mode at the charge-pump output.
FIG. 3 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,734,279. The circuit of FIG. 3, similar to the circuit of FIG. 2, is limited to the speed of PMOS transistors M1 and M2 used in the pull-up stage. Furthermore, the conventional charge-pump shown requires extra circuitry to maintain an adequate common mode at the charge-pump output.
FIG. 4 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,734,279. The circuit of FIG. 4, similar to the circuits of FIG. 2 and FIG. 3, is limited to the speed of PMOS transistors M9-M10 used in the pull-up stage. Furthermore the conventional charge-pump shown requires extra circuitry to maintain an adequate common mode at the charge-pump output.
FIG. 5 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,239,455.
FIG. 6 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,663,686. The circuit of FIG. 6 requires extra circuitry to maintain an adequate common mode at the charge-pump output and precise matching between pull-up and pull-down currents. It also is very sensitive to the matching of CMOS transmission gate impedances.
FIG. 7 illustrates a conventional charge-pump circuit that can be found in U.S. Pat. No. 5,625,306. The circuit of FIG. 7, similar to the circuit of FIG. 6, requires extra circuitry to maintain an adequate common mode at the charge-pump output and precise matching between pull-up and pull-down currents.